In industries, it is getting required to further upgrade the dimensional accuracy, the roundness, or the like of bar stocks, wire stocks, or the like, having circle shapes in their transverse cross sections. For example, in the case of a steel stock having a diameter of about 50 mm, it is required that the steel stock has a dimensional tolerance value, a value of the difference between the maximum diameter and the minimum diameter in the same cross section, or the like, in a range of plus/minus 0.70 to 0.80 mm in the conventional Japanese Industrial Standard (hereinafter simply referred to as "JIS"). However, it has been required recently that the steel stock has the dimensional tolerance value, the value of the difference, or the like, falling in the the higher accuracy, e.g., in a range of plus/minus 0.10 to 0.20 mm.
Accordingly, instead of the conventionally employed HV (i.e., horizontal and vertical) type roll apparatus for rolling in which two rolls are disposed vertically, the present applicant introduced an apparatus which is adapted for precision rolling or ultra precision rolling steel stocks into its manufacturing line. The precision or ultra precision rolling apparatus comprises a plural set of 3-roll apparatuses which are disposed in series in a steel stock transferring direction and which include 3 rolling rolls. The 3 rolling rolls have a caliber groove surface going therearound in a ring shape, and they are disposed at equal intervals in a circumferential direction of a steel stock. With this apparatus, it is possible to make the dimensional accuracy, the roundness, or the like, of the steel stock further accurate.
In this apparatus adapted for precisely or ultra-precisely rolling the steel stock, there is installed a sizing apparatus which is adapted for shaping at the final process of the rolling process. The sizing apparatus also comprises a plural set of 3-roll apparatuses which include 3 sizing rolls. Likewise, the 3 sizing rolls have a caliber groove surface going therearound in a ring shape, and they are disposed at equal intervals in the circumferential direction of the steel stock. Likewise, in the sizing apparatus, it is needed to dispose a plural set of the 3-roll apparatuses in series in the steel stock transferring direction. Moreover, on an outlet side of the sizing apparatus, it is necessary to install a guide apparatus having a guide bore in order to guide the steel stock, which has been subjected to the sizing and which has been discharged from the outlet side of the sizing apparatus, to a subsequent process.
In the sizing apparatus which is employed in the final process of the precision or the ultra precision rolling apparatus, the depressing rate reduction is extremely small during the sizing. Consequently, there is provided an advantage that the steel stock sized with the sizing apparatus comes to exhibit the dimensional accuracy, the roundness, or the like in high precision. However, there arises a problem that the leading end of the thusly sized steel stock is likely to bend in a letter "S" shape, usually in a letter "S" shape which is bent 3-dimensionally. When the depressing rate is increased during the sizing with the 3-roll apparatuses, the steel stock comes to be depressed heavily by heavily bringing all of the caliber groove surfaces of the 3 sizing rolls constituting the 3-apparatuses into contact with the outer peripheral surface of the steel stock, and accordingly the depressing is developed to the central portions of the steel stock. As a result, a balance is attained in the depressing, and the letter "S" shaped bending is relieved. However, the steel stock hardly comes to exhibit the dimensional accuracy, the roundness, or the like in high precision. Thus, the heavy depressing with the sizing apparatus does not conform to the precision or the ultra precision rolling.
When the leading end of the steel stock is bent in a letter "S" shape as aforementioned, it is troublesome to transfer the steel stock to a subsequent process. Moreover, the leading end bent in a letter "S" shape can hardly be a product in view of quality, and it should be cut accordingly. Thus, the bent leading end causes a limit in the improvement of material loss.
It is believed that the "S" shaped bending is caused as follows. Namely, in the sizing apparatus employed in the final process of the precision or the ultra precision rolling apparatus, the depressing rate is adjusted to an extremely small value during the sizing in order to keep the dimensional accuracy, the roundness, or the like, of the steel stock high. Consequently, in the final 3-apparatus of a plural set of the 3-roll apparatuses constituting the sizing apparatus, e.g., the 3-roll apparatus disposed most adjacent to the outlet side of the sizing apparatus, there is a sizing roll whose caliber groove surface is heavily brought into contact with the steel stock, and there are sizing rolls whose caliber surfaces are weakly brought into contact with the steel stock. With this arrangement, the sizing roller whose caliber groove surface is heavily brought into contact with the steel stock works to extend the surface of the steel stock, and the sizing rollers whose caliber groove surfaces are weakly brought into contact with the steel stock do not work to extend the surface of the steel stock and their depressing do not reach the central portions of the steel stock. As a result, the depressing balance to be ensured in the 3-roll apparatus is likely to collapse at the leading end of the steel stock. When the depressing balance is collapsed in this way, the surfaces which have been heavily brought into with each other vary their curvature directions subsequently so as to avoid the collapsed depressing balance, and they vary their curvature directions until the other balance is attained. Consequently, it is believed that the steel stock is bent in a letter "J" shape at the leading end at first, and that the steel stock is bent in the letter "S" shape eventually.
For reference, there have been disclosures on apparatuses for guiding steel stocks so far. For example, Japanese Unexamined Utility Model Application No. 106,518/1988 discloses a steel stock guide apparatus in which a front member of a nozzle is formed of ceramics and a rear member of the nozzle is formed of metal, and Japanese Utility Model Application No. 192,467/1986 discloses a steel stock guide apparatus which comprises an outer layer including metal and an inner layer including ceramics, whereby enhancing the seizure resistance and the wear resistance. However, although there is provided an advantageous effect that the steel stock can be guided to a subsequent process with these steel stock guide apparatuses, no effect on "S" shape bending reduction is expected therefrom.
The present invention has been developed in view of the "S" shape bending problems which inherently occur when the sizing operation is carried out with the above-described 3-roll type sizing apparatus so as to achieve the high accuracy. It is therefore an object of the present invention to provide a steel stock shaping apparatus, especially a sizing apparatus, and a steel stock shaping process which enable to relieve or avoid the "S" shape bending occurring at a leading end of a steel stock.